Practical, sustainable, wide-temperature-adaptable zinc-metal batteries enabled by electrogelated recyclable biomacromolecular hydrogel electrolytes

Abstract In the promotion of aqueous zinc (Zn)-metal batteries, hydrogel electrolytes have been found to come with the capability to physically obstruct dendritic Zn growth and suppress unwanted side reactions compared to their liquid counterparts. However, due to the opposite structural requirements for ionic conductivity and mechanical strength, the preparation of thin-film hydrogel electrolytes for energy-dense Zn-metal batteries remains a formidable task. Herein, electrogelation that offers several unique advantages, including precise control over the thickness, good geometric adaptability, and high tunability of the hydrogels’ microstructures and properties, is investigated as a promising technique to address the above-mentioned dilemma. It is shown that, by varying the electrogelation parameters, various biomacromolecular hydrogel electrolytes featuring highly micro-/nanostructured pores are obtained to deliver simultaneously high mechanical strength (2.0 to 4.4 MPa) and high ionic conductivity (10.1 to 19.5 mS cm−1). Such in situ built electrolytes can be as thin as 50 μm and enable excellent Zn plating/stripping reversibility at 1 mA cm−2/1 mAh cm−2 with Coulombic efficiency averaging 99.83% for over 2800 cycles (> 6 months); the Zn-metal battery with a high-areal-capacity of 5.4 mAh cm−2 and a practical negative-to-positive capacity ratio of 1.1 retains 70% of its initial capacity after 120 cycles. We quantitatively show the respectable recyclability, low environmental impact, and cost-effectiveness of our biomacromolecular hydrogel electrolytes by integrating experimental study, life-cycle assessment, and techno-economic analysis, opening the door for the research of more sustainable Zn-metal batteries and beyond.